The present invention relates to a nonaqueous secondary battery having improved charge-discharge capacity and cycle characteristics.
Representative examples of negative electrode material for nonaqueous secondary battery include lithium metal and lithium alloy. However, the use of such a negative electrode material involves a risk of internal shortcircuiting caused by the production of so-called dendrite, i.e., branched lithium crystal during charging/discharging or ignition attributed to the high activity of dendrite itself.
On the other hand, a calcined carbonaceous material capable of reversibly intercalating/deintercalating lithium has been recently put into practical use. Such a carbonaceous material has disadvantage that it has a relatively low density and therefore a low capacity per unit volume. Pressing or lamination of a carbonaceous material with a lithium foil is disclosed in JP-A-5-151995 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). However, this approach cannot give an essential solution to the foregoing problems due to the foregoing disadvantage.
Further, the use of an oxide of Sn, V, Si, B, Zr or the like or a composite oxide thereof has been proposed (JP-A-5-174818, JP-A-6-60867, JP-A-6-275267, JP-A-6-325765, JP-A-6-338324, EP-615296). It is said that the combination of a negative electrode comprising such an oxide or composite oxide with a positive electrode comprising a certain kind of a transition metal compound containing lithium can give a 3-3.6 V class nonaqueous secondary battery having a great charge capacity which shows little or no production of dendrite in practical use to give an extremely high safety. However, batteries comprising these materials have greatly disadvantage in that they exhibit insufficient charge-discharge cycle characteristics, particularly a low charge-discharge efficiency in the initial cycle. In other words, it can be presumed that a part of lithium which has been intercalated in the negative electrode during the charging process undergoes a plurality of irreversible side-reactions that prevent lithium from migrating toward the positive electrode during the discharging process, resulting in idle consumption of lithium in the positive electrode that causes capacity loss. In order to make up for the capacity loss, it has been proposed that lithium be previously intercalated in the negative electrode material in an amount corresponding to the loss. However, satisfactory effects have never been obtained yet.
Therefore, an object of the present invention is to provide a nonaqueous secondary battery having (1) high charge-discharge capacity and good charge-discharge cycle characteristics and (2) a high energy density.
The foregoing object of the present invention is accomplished with nonaqueous secondary batteries according to the following items.
(1) A nonaqueous secondary battery comprising a positive electrode sheet having a layer mainly comprising a lithium-containing metal oxide, a negative electrode sheet having a negative electrode material mixture layer mainly comprising a negative electrode material laminated with a metallic material mainly comprising lithium, a nonaqueous electrolytic solution containing a lithium salt, and a separator, wherein the nonaqueous secondary battery is prepared by a process which comprises winding the positive electrode sheet, negative electrode sheet and separator; inserting the elements thus wound into a battery can; injecting the electrolytic solution into the battery can, sealing the battery can, ageing the battery at a low temperature, charging or discharging the battery, and then ageing the battery at a high temperature.
(2) The nonaqueous secondary battery as in the above item (1), wherein the negative electrode sheet is one comprising a layer mainly comprising an oxide or chalogenide of a metallic or semi-metallic element and at least one auxiliary layer containing an electrically-conductive water-insoluble particle laminated with a metallic material mainly comprising lithium.
(3) The nonaqueous secondary battery as in the above item (2), wherein the temperature at which the low temperature ageing is effected is from 2xc2x0 C. to 30xc2x0 C.
(4) The nonaqueous secondary battery as in the above item (1) or (2), wherein the charging or discharging before the high temperature ageing causes the open-circuit voltage of the battery to be from 2.5 V to 3.8 V.
(5) The nonaqueous secondary battery as in the above item (4), wherein the charging or discharging before the high temperature ageing is effected within 60 days after sealing.
(6) The nonaqueous secondary battery as in the above item (5), wherein the temperature at which the high temperature ageing is effected is from 40xc2x0 C. to 70xc2x0 C.
(7) The nonaqueous secondary battery as in the above item (6), wherein the duration of the high temperature ageing is from 1 hour to 40 days.
(8) The nonaqueous secondary battery as in the above item (5), wherein the charging process is a constant electrical quantity charging process and the electrical quantity used is from 40 mAH to 400 mAH.
(9) The nonaqueous secondary battery as in any one of the above items (5) to (8), wherein the charge-discharge process involves a constant voltage charging process which terminates at a voltage of from 2.0 to 3.8 V and a constant current discharging process which terminates at a voltage of from 1.0 to 3.5 V and the number of charge-discharge cycles is from 1 to 500.
(10) The nonaqueous secondary battery as in any one of the above items (1) to (9), wherein the negative electrode is made of a composite oxide or chalcogenide containing tin.
(11) The nonaqueous secondary battery as in the above item (10), wherein the composite oxide or chalcogenide containing tin is a compound represented by formula (1):
SnM1aOtSuxe2x80x83xe2x80x83(1)
wherein M1 represents two or more elements selected from the group consisting of Al, B, P, Si, Ge, elements belonging to the groups I to III in the periodic table, and halogen elements; a represents a number of from 0.2 to 2; t represents a number of from 1 to 6; and u represents a number of not more than 0.5.
(12) The nonaqueous secondary battery as in the above item (11), wherein the composite oxide or chalcogenide containing tin is a compound represented by formula (3):
SnM3cM4dOtSuxe2x80x83xe2x80x83(3)
wherein M3 represents at least one element selected from the group consisting of Al, B, P, Si and Ge; M4 represents at least one element selected from the group consisting of elements belonging to the groups I to III in the periodic table, and halogen elements; c represents a number of from 0.2 to 2; d represents a number of from 0.01 to 1; t represents a number of from 1 to 6; and u represents a number of not more than 0.5, with the proviso that c and d satisfy the relationship of 0.2 less than c+d less than 2.